While rechargeable batteries are well recognized for the vital role they play in mobile communications, rechargeable batteries may also be a potential replacement for conventional combustion engines in a variety of electric vehicles, including automobiles, airplanes, and boats. The U.S. Department of Energy's proposed roadmap for rechargeable batteries recommends a ten-fold rise in energy density, from 150 Watt-hours per kilogram (Wh/kg) to 3,000 Wh/kg. The roadmap further recommends a one-third reduction in the price per kilowatt hour (kWh) (from $300/kWh to $100/kWh) of the battery, with the improvements in density and cost-savings to be realized by 2020.